Geophysical turbulence

Abstract

A novel design of a piezoelectric silicon micropump is proposed, which provides a constant flow rate over a wide backpressure range of up to 30 kPa. This highly appreciable feature is based on a new serial arrangement of two active valves and relies on both an appropriate electrical actuation sequence of the piezo-actuators and an immanent limitation of the membrane deflection by the valve seats. The design is optimized for the low flow regime ranging from 0.1 to 50 µl min −1 . A detailed lumped-parameter model is derived in order to reveal the physics behind this pumping principle and to identify the optimum control scheme. For the fabrication of our device, a comparably simple and robust 2-wafer process is utilized. A thorough experimental investigation demonstrates the high performance of the micropump. The backpressure independence of the flow rate enables high-resolution volumetric dosing within the aforementioned flow range. The stroke volume and hence the resolution of the micropump is adjustable via the upstroke voltage of the actuator between 50 and 200 nl. Depending on this setting typical actuation frequencies range from 0.05 to 5 Hz and the flow rate scales proportional to the frequency within that frequency range.

Statistical properties of turbulence: An overview

“…A naïve pseudospectral method cannot be used for the FENE-P model given in Eqs. (18) and (19): the polymer conformation tensor C is symmetric and positive definite; however, in a practical implementation of the pseudo-spectral method it loses this property. We have employed a numerical technique that uses a Cholesky decomposition to overcome this problem; we refer the reader to Ref.…”

“…Mathematical questions in this area are concerned with developing proofs of the smoothness, or lack thereof, of solutions of the Navier-Stokes and related equations [6][7][8][9][10]. Turbulence also provides a variety of challenges for fluid dynamicists [5,[11][12][13], astrophysicists [14][15][16][17], geophysicists [18,19], climate scientists [20], plasma physicists [15][16][17]21,22], and statistical physicists [23][24][25][26][27][28][29][30][31][32]. In this brief overview, written primarily for physicists who are not experts in turbulence, we concentrate on some recent advances in the statistical characterisation of fluid turbulence [33] in three dimensions, the turbulence of passive scalars such as pollutants [34], two-dimensional turbulence in thin films or soap films [35,36], turbulence in the Burgers equation [37][38][39], and fluid turbulence with polymer additives [40][41][42]; in most of this paper we restrict ourselves to homogeneous, isotropic turbulence [33,…”

The Dark Matter and Energy in the De Sitter World

“…The last conclusion follows from the fact that according to the standard cosmological model, the de Sitter world is a necessary phase of the evolution of the universe in the first instants (10 -34 -10 -32 seconds) after the Big Bang, (see reviews on cosmology in [22,23]).…”

“…Of course, our universe is not the de Sitter's world, although according to some data it is developing in the direction of this model, [22]. Considering the given phenomena of dark matter and dark energy in the general case is a difficult task because today there is no quantum theory of gravity.…”